[Hillarys Gate Cult]

For something as large as an artillery shell, wouldn't the rifling grooves be pre-cut onto the shells?

That's what the copper band is for. The shell's hard metal casing would destroy the rifling on the barrel after only one firing. Plus a shell made exactly to the size of the barrel could jam. Swiss Precision would be needed on every shell. The copper band is made smooth to follow the rifling grooves of the barrel, keep the round stable, and reduce barrel wear. It's engineered to use the bare minimum of copper needed. That's definitely a fired artillery round, of what exact size I'm not sure.

[CarrotAndStick]

Thanks for the information! I was thinking if the shells didn't have grooves pre-cut on them, they'd jam inside the barrel. Silly me.